How to Interpret Data for Overly Rich Air-Fuel Mixture?
2 Answers
When the air-fuel mixture is overly rich, the onboard computer becomes ineffective and cannot display data. The following methods can be used for diagnosis: 1. Immediate Engine Stalling: This method is based on the theory that during idle, if the vacuum hose is suddenly disconnected and the engine stalls immediately, it indicates a lean air-fuel mixture. 2. Smoother Engine Operation: If the engine runs more smoothly than before, with a significantly higher but unstable idle speed, it suggests a rich air-fuel mixture. 3. Minimal Engine Change: If the engine speed does not increase (or increases slightly), with an idle that is somewhat unstable but close to normal, it indicates a properly balanced air-fuel mixture.
To diagnose a rich air-fuel mixture, I typically use an OBD scanner to read the engine's data stream. Pay attention to the oxygen sensor's voltage reading—if it consistently stays above 0.5V, the mixture might be too rich, as normal readings should fluctuate between 0.1V and 0.9V. Also, check the short-term fuel trim value. If it's negative, say -10% or lower, it indicates the system is reducing fuel supply to compensate for the rich condition. This could be caused by a clogged air filter or excessive fuel pressure, which I've encountered in my own car. Cleaning the filter or inspecting the fuel pump often resolves the issue. Ignoring it long-term can significantly increase fuel consumption and emissions, costing more money and harming the environment. Regular checks with simple tools can prevent major problems.
